I was looking at the UC3C-EK schematics VCC5:
First there is an incorrect notice:
All on-board components are powered by 3,3V
(Only LCD back light is powered by VCC5)
The ATA6660 is specified for a TXD minimum of 2 volts high input and the 3.3 volt UC3C Tx_CAN_0 PB5 high output is 2.5 volts minimum. This works, but is only a 1/2 volt design noise margin.
The Rx_CAN_1/PC11 connection also has this same over the absolute maximum violation problem.
There is no voltage divider or even current limiting resistor shown for the Rx_CAN_0/PB4 or Rx_CAN_1/PC11 connections.
Am I crazy or has ATMEL actually designed a board that violates the UC3C absolute maximum pin input voltage for port pins PB4 and PC11? I did not see any special UC3C data sheet electrical characteristics that made any specification exception for the alternate use CAN pins. Did I miss something?